1. Field of the Invention
The present invention relates to a semiconductor device including a plurality of circuit elements arranged in matrix.
2. Description of the Related Art
There is known a technique for driving a plurality of circuit elements that are arranged in matrix and includes a selection transistor with a plurality of signal lines and a driver circuit. Such a technique is applied, for example, to image display devices such as liquid crystal display devices, light-emitting display devices, and electronic paper and storage devices such as DRAM and SRAM.
An n-channel transistor is often used as the selection transistor. Some of the reasons are as follows: an n-channel transistor operates at high speed because electrons with high mobility are used as carriers, and is suitable for miniaturization because large current can flow through even a relatively small n-channel transistor.
Application of such a technique to image display devices is generally referred to as an active matrix technology or the like. For example, most of active-matrix liquid crystal display devices include a pixel portion including n-channel transistors.
Storage devices using semiconductor elements are broadly classified into two categories: a volatile storage device that loses stored data when power supply stops, and a non-volatile storage device that holds stored data even when power supply stops.
A typical example of a non-volatile storage device is flash memory. Flash memory holds electric charge in a floating gate and thus has a semi-permanent data retention time (e.g., see Patent Document 1). However, flash memory consumes large power because it requires high voltage for writing and erasing data, and in addition, it is not easy to increase the speed of these operations.
Typical examples of volatile storage devices are dynamic random access memory (DRAM) and static random access memory (SRAM). Such volatile storage devices lose stored data when power supply stops, but consume relatively less power because they do not need high voltage as in non-volatile memory.
In recent years, development of devices for which low power consumption is required, for example, portable electronic devices such as mobile phones and small computer and wireless devices to which power is wirelessly supplied, such as non-contact IC cards and RFID tags, has progressed. In such devices, even a slight increase in power consumption sometimes becomes problematic. The increase in power consumption leads to a reduction in the communication range in RFID tags, and leads to a reduction in the driving time with a battery in portable phones, for example.